Electromechanical delay line

ABSTRACT

An electromechanical delay line comprising an acoustic line, an input and an output piezoelectric transducer, secured to the end faces of the acoustic line by means of a coupling medium, wherein the ratio between the acoustic resistance of the material of the piezoelectric transducer and that of the acoustic line material is selected equal to 0.55 - 0.95, the ratio of the thickness of the coupling medium to the wavelength in the medium at the resonance frequency of the piezoelectric transducers is selected equal to 0.005 - 0.05, and the ratio of the area of each piezoelectric transducer, adjacent to the respective end face of the acoustic line, to the area of this end face is selected equal to 0.75 - 1.00 so that maximum bandwidth of the delay line is provided.

1 I; A: ijnited Stat 2 i a J 1111 3,796,974 Khanovich et a1. Mar. 12, 1974 ELECTROMECHANICAL DELAY LINE [76] Inventors: Izrail Grigorievich Khanovich,

ploschad Chernyshevskogo, 10, kv.

[21] Appl. No.1 281,020

25; Robert Avgusmvich Raudson, 52 Us. 01. 333/30, 310/8.3, 310/91 Krasnogvardeiskaya ploschad 1 kv [51] Int. Cl. 03h 7/30 42; M Saukwich Pol-moi, ulitsa [58] Field of Search 333/30; 310/83, 9.] Smirnova, 26, kv. 16; Gennady Grigorievich Yanovsky, Mokhovaya [56] References Cited litsa, 34; {Walla UNITED STATES PATENTS Alexandmvna Komsskaya 7 3,593,214 7 1971 Cooper 333/30 Lakhtinskaya ulitsa, 22, kv. 13;

3,665,225 5/1972 Owen et al 333/30 Avr-aam sered'nsky uhtsa 3,687,697 8/1972 Faulstich et a1. 333 30 Babushkma, 72; Robe" 3,702,448 11/1972 Boble tt 333 30 Ivanovich Kapranov, P p 3,582,834 6/1971 Evans 333/30 Gorkogo, 73/39, kv. 19; Felix Fomich Molokov ulitsa I Primary ExaminerRudolph V. Rolinec Besmzhevslfaya 9; F Assistant Examiner-- Saxfield Chatmon, Jr. a d vt h Bqgachev, uhtsa Attorney, Agent, or FirmWaters, Roditi & Schwartz Varshavskay, 58, kv. 28; Jury Grigorievich Sergeev, prospekt Kosmonavtov, 52, korpus 4, kv. 43; i [57] ABSTRACT Alexandra Fed n Z kha An electromechanical delay line comprising an acousulit a Leni 28, k 19, ll f tic line, an input and an output piezoelectric trans- Leningrad; Ni G i i ducer, secured to the end faces of the acoustic line by Chomova, ulit T l likhi 1/2 means of a coupling medium, wherein the ratio bekv, 237 M w; R i Gi h i h tween the acoustic resistance of the material of the pi- Brit i h k kt s h 34 ezoelectric transducer and that of the acoustic line kv, 50; Al nd M d kh i h material is selected equal to 0.55 0.95, the ratio of Ne omnyasch lit s d the thickness of the coupling medium to the wave- 122, kv. 9, both of Leningrad; length in the medium at the resonance frequency of Vl di i Nikif i h Zh hi the piezoelectric transducers is selected equal to 0.005 ulitsa s k 2/102, hr, 27; 0.05, and the ratio of the area of each piezoelectric Valentin V ili i h T ili li transducer, adjacent to the respective end face of the Krasn 40, k 5, b h f acoustic line, to the area of this end face is selected El kt t l M k k i bl i ll equal to 0.75 1.00 so that maximum bandwidth of of USSR, the delay-line is provided.

[22] Filed: Aug. 16, 1972 1 Claim, 4 Drawing Figures PATENTEDHAR 12 I974 SHEET 2 BF 2 Q g i ELECTROMECHANICAL DELAY LINE The present invention relates to delay lines and, more specifically, to electromechanical delay lines intended for use in construction of computers, radar and television equipment, for example, in colour T.V. receivers.

Electromechanical delay lines comprising a glass acoustic line and piezoelectric transducers brazed or pasted to its end faces by means of a coupling medium have been previously described (see, for instance, USSR Patent Application of the company Telefunken filedin the USSR in 1967 under the title Electromechanical delay device).

These lines did not use the optimum range of parameter variations which provides a broad passband of the line; in particular, the ratio of the acoustic resistances of the piezoelectric transducer-and the acoustic line materials amounted to ===1.8.

The disadvantage of these known lines is their narrow band-width, the ratio of the bandwidth to the resonance frequency of the piezoelectric transducer not exceeding 0.3-0.4.

An object of this invention is to eliminate the above disadvantage.

This invention is aimed at providing such relationships determining the bandwidth of an electromechanical delay line as to obtain the maximum bandwidth of the line.

To accomplish the foregoing object, in an electromechanical delay line comprising an acoustic line, an input and an output piezoelectric transducer secured to the end faces of the acoustic line by means of a coupling medium, according to the present invention, the ratio between the acoustic resistance of the piezoelectric transducer material and that of the acoustic line material is selected equal to 0.55-0.95, the ratio between the coupling medium thickness and the elastic wave length in its material at the resonance frequency of the piezoelectric transducers is selected equal to 0.0050.050, and the ratio of the area of each piezoelectric transducer to the respective area of the end face of the acoustic line is selected equal to 0.75-1.00.

This permits maximum expansion of the bandwidth of the electromechanical delay line.

The present invention may be more fully understood from the following description of a preferred embodiment thereof when read with reference to the accompanying drawings wherein:

FIG. 1 is a schematic diagram of an electromechanical delay line;

FIG. 2 represents relative bandwidth A f f versus coupling medium thickness 1 A for k 1.6 and k 0.7;

FIG. 3 shows the optimum ratio of the coupling medium thickness to the elastic wave length in this medium at the resonance frequency of the piezoelectric transducer versus the ratio of the acoustic resistances of the piezoelectric transducer and coupling mediums;

FIG. 4 represents a relative bandwidth of the piezoelectric transducer versus dimensionless likelihood factor The delay line disclosed herein can operate in various 7 devices as a passive balanced four-terminal network whose terminals on one side are used for receiving an electric signal, and on the other side, for giving out a time-delayed signal.

' where C velocity of elastic waves in the coupling The delay line consists of an acoustic line 1 F IG. 1 piezoelectric transducers 2 secured to the end faces of the acoustic line 1 by means of a coupling medium 3 which may be brazing solder or adhesive; signalling electric terminals 4 attached to the external sides of the piezoelectric transducers 2 and earthing terminals 5 and a coating 6 which serves for suppressing spurious signals reflected from the end faces of the acoustic line 1.

Let us designate the acoustic resistances of the line component mediums, respectively, as follows:

Z, acoustic resistance of the material of the acoustic line 1;

Z acoustic resistance of the material of the piezoelectric transducers 2;

Z, acoustic resistance of the coupling medium 3;

Z acoustic resistance of the material of the coating 6, and their relationships, respectively:

As has already been shown, one of the characteristics defining the bandwidth of an electromechanical delay line is ratio k; of the acoustic resistances of the materials of the piezoelectric transducer'Z and the acoustic line 1Q As a result of theoretical and experimental studies of delay lines used for various applications, the-inventors were first to demonstrate that the maximum bandwidth values: 0.95 0.98 (nonsymmetrical load of the piezoelectric transducer) and 1.40 1.45 (symmetrical loads of the piezoelectric transducers) are attained with k 0.55 0.95 if at the same time a relative thickness of the coupling medium is chosen within the above optimum range.

FIG. 2 represents the relationship between relative bandwidth Af:f andrelative thickness of the coupling u medlum I3 I X30 162.3 52 kgq For example, let the material of the piezoelectric transducer 2 be lead zirconatetitanate, and the materials of the coupling medium 3 and the acoustic line 1 four-component solder and carbon tool steel, respectively.

Acoustic resistances of these materials are as follows:

Z, 0 (in case of a nonsymmetrical load of piezoelectric transducers);

Z 1.8 10 gem sec Z, 2.56 10 g. cm sec Then, the ratios of the acousticresistances are as follows: k 0; k 0.7; k 1.63. Below is given the procedure for calculating the optimum thickness of the coupling medium 3. Wavelength X 30 in the coupling medium 3 at the resonance frequency of the piezoelectric transducer 2 is given by the formula:

medium 3. The curve showing the optimum value (1 A opt providing the maximum relative bandwidth versus k is illustrated in FIG. 3 for the case of a non symmetrical load of the piezoelectric transducer 2 (k 0) with the optimum ratio k 0.7.

At the resonance frequency of the piezoelectric transducer f 4.3 MHz and C 1.6. 10 cmsec, elastic wave length) F 370 microns. As can be seen from'FlG. 3, it corresponds to (1 )t opt 1/50 and, consequently, I 7.5 microns. Delay lines with the above characteristics, namely: k 0.7; (1 A opt 1:50, but with the ratio of the area of the piezoelectric transducer to that of the end face of the acoustic line equal to from 0.7 to 0.9 have bandwidth Af equal to from 3.4 to 3.8 MHz as demonstrated by test results. Consider now an example of selecting the optimum area of the piezoelectric transducer 2.

A relative bandwidth of each piezoelectric transducer 2 (FIG. 4) defined by ratio Af/f where Af bandwidth, and f resonance frequency of the piezoelectric transducer 2, is a monotonically increasing function of the dimensionless generalized parameter x (eS/a") CR where e dielectric constant of the material of the piezoelectric transducer 2;

S area of the piezo element of the piezoelectric transducer 2;

a' thickness of the piezo element;

C velocity of elastic waves in the material of the piezoelectric transducer 2;

R electrical load resistance.

In FIG. 4, the solid curve is the relation Af/fi, (x) derived by the inventors by theoretical calculations, while various individual points represent the results of experiments with piezoelectric transducers made from different materials and having different thickness of material and the area of the piezoelectric transducer 2.

From consideration of FIG. 4 it follows, in particular, that for increasing the bandwidth ofa delay line it is required to increase as much as possible the area of the piezoelectric transducer 2 secured to the end face of the acoustic line 1 so that it is equal to the area of the end face of the acoustic line.

It has been shown experimentally that in delay lines, for instance, those employed in colour television receivers, a decrease of the surface of the piezoelectric transducer 2 below 0.75 of the end face of the acoustic line 1 brings about a significant narrowing of the bandwidth. Thus, if 0 0.005-0.050 and k 0.55 0.95, but the ratio of the area of each piezoelectric transducer 2 to that of the adjoining end face of the acoustic line equals 0.65, the bandwidth of the delay line 1 narrows to 2.5 2.8 MHz at the same resonance frequency of the piezoelectric transducer 2 as in the previous example.

In conclusion, here is anexarnple of how to make simultaneous selection of all the three optimum characteristics, namely, 0.7, 1 A 0.020 and the ratio of area S of the piezoelectric transducer 2 to that of the end face of the acoustic line equal to 1. In this case, delay lines for use in colour television receivers (f 4.3 MHz) have bandwidth Af= 4MHz, consequently, ratio A f f is very close to the theoretically-derived optimum value 0.98 for a non-symmetrical load of the piezoelectric transducer 2.

What is claimed is:

1. An electromechanical delay line comprising an acoustic line, a coupling medium, and input and output piezoelectric transducers secured to the end faces of said acoustic line by means of said coupling medium, wherein the ratio between the acoustic resistance of the material of said transducers and that of the material of said acoustic line is chosen to be 0.55 0.95, the ratio of the thickness of said coupling medium to the elastic wave length in said coupling medium at the resonance frequency of said transducers is chosen to be 0.005 0.05, and the ratio of the area of each transducer, adjacent to the respective end face of said acoustic line, to the area of the end faces is chosen to be 0.75 1.00. 

1. An electromechanical delay line comprising an acoustic line, a coupling medium, and input and output piezoelectric transducers secured to the end faces of said acoustic line by means of said coupling medium, wherein the ratio between the acoustic resistance of the material of said transducers and that of the material of said acoustic line is chosen to be 0.55 - 0.95, the ratio of the thickness of said coupling medium to the elastic wave length in said coupling medium at the resonance frequency of said transducers is chosen to be 0.005 - 0.05, and the ratio of the area of each transducer, adjacent to the respective end face of said acoustic line, to the area of the end faces is chosen to be 0.75 - 1.00. 